Download Geoid Isostasy

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Geoid
•  Equipoten0al
surface
–
surface
with
the
same
poten0al
energy
–  Geoid
–
The
gravita0onal
equipoten0al
surface
corresponding
to
mean
sea
level,
including
the
level
at
which
the
sea
would
stand
in
a
con0nental
area
if
it
were
able
to
do
so.
–  Spheroid
–
mathema0cal
representa0on
of
sea‐level
with
all
irregular
influences
removed
–  Gravity
anomalies
–
The
gravita0onal
accelera0on
remaining
aEer
allowing
for
other
factors
0.875
km
–
average
eleva0on
of
con0nents
3.729
km
–
average
depth
of
the
ocean
floor
Isostasy
•  The Earthʼs crust adjusts to changes in mass that occur
in the earth surface
•  Equilibrium within the Earthʼs crust –  Forces acting to elevate landmasses are balanced by
forces acting to depress them
–  e.g. Ice sheets, mountain building
•  Lithospheric plates “float” at a given elevation depending
on their thickness
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Endogenic vs Edogenic
geomorphic processes
Exogenic – surfacial
• 
• 
• 
• 
• 
• 
Weathering and erosion
Glaciation
Eolian (wind driven)
Biological
Hydrologic cycle
Anthropogenic/animal
•  Endogenic: “from the inside”
–  formed beneath the surface of the Earth
•  Volcanism: hotspot activity, sea-floor spreading, volcanic
arcs
•  Seismicity/Plate Tectonics
•  Regional uplift and subsidence
What do we mean by structural control on
geomorphic processes?
•  Structural and
stratigraphic arrangement
of rock layers and
masses
•  Previous tectonic
displacement
•  Present state of
deformation
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Soils
Climate
•  Establishes the temperature and moisture
conditions at and near the earthʼs surface
–  Most important long-term control of
weathering processes
–  Driven by solar radiation
•  Worldwide pattern of soil types reflects
climate zonation
–  Arid regions – very little rainfall
•  Limited contact time between soil and water
–  Limits chemical weathering
•  Mid-latitude deserts
–  Temperatures are high,
precip is low  chemical
weathering slow
•  Thin, carbonate rich soils
•  Humid, high latitude
–  Low temps, moderate precip
•  Intermediate soils
•  Polar regions
–  Low temp and low precip
•   poor soil development
•  Humid regions
–  Materials (soil, rocks, etc)
are in contact with moisture
for long periods of time
•  Increased chemical and
physical weathering
–   Intense leaching and
deep weathering
•  Tropics
–  High humidity and high
temperatures
•  Intense weathering
–  Produces red soils
–  High amounts of iron
and aluminum oxides
Vegetation and climate
•  Vegetation affects the amount of water
that permeates into the ground versus the
amount that runs off the surface
•  Heavy vegetation  less runoff, more
water enters soil
–  Chemical weathering more effective
•  Sparse vegetation  high runoff, less
water enters soil
–  Chemical weathering less effective
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Vegetation and soil
•  Humid regions
–  Water retention promotes chemical
weathering
–  Root action promotes mechanical weathering
–  Organic acids chemically attack rocks
–  Organic material from decaying plants added
to soils
•  Climate affects
environmental factors
which in turn affect
processes
•  Ex. Sea-Level
Fluctuation
–  Base-level
–  Eustatic change –
water level rise or fall
24,000
year
History
of
Sea
Level
Rise
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